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Thread: White Smoking Knuckle

  1. #1

    White Smoking Knuckle

    Hi Guys.

    Just finished the old 41 and have just managed to get the timing right.
    Have been riding her a couple of times around the farm and I get the problem almost right away when it gets hot, white thick smoke/ and it smells of oil.
    Been reading about different oil issues, wrong installation of wrist pin, rings, guides etc.
    Im not quite sure. but I personally think the problem could be the oil pump filling up the crank case...Sylinders are redone with new pistons and rings, heads redone at a machine shop,the pump is a new replica without the governor rotor, the pump that came in 1948.
    Could it be that the crank case is getting filled up???
    Greate if you guys got a link or something to how to adjust pump or to check if the crank case is being filled up cause I cant find it
    Sylinders are redone with new pistons and rings, heads redone at a machine shop.


  2. #2
    Join Date
    Apr 2010
    Western Oregon

    Re: White Smoking Knuckle

    If the rocker tins are not draining it will cause this problem, the tins fill and oil enters the valve guide and burns in the combustion chamber causing lots of smoke .

  3. #3

    Re: White Smoking Knuckle

    Thanks for the reply ultrapan.
    I will have a check and see, quite new with knucks-but are the tins getting emptied due to vacuum in the lines?

  4. #4

    Re: White Smoking Knuckle

    or to check if the crank case is being filled up cause I cant find it
    Remove drain plug in left case when it smokes to check crankcase oil.

    I will have a check and see, quite new with knucks-but are the tins getting emptied due to vacuum in the lines?
    Oil is sucked from valve covers through valve cover lines, passage in case, then through breather.
    Valve cover lines have to be clean, case passage clean, breather timed, correct breather with hole to suck.
    Last edited by 1950panhead; 08-28-2016 at 07:35 AM.

  5. Re: White Smoking Knuckle

    Does "replica" mean Tedd's?

  6. #6

    Re: White Smoking Knuckle

    Are you certain the smoke is white ? In the old days, white was water, blue was oil, and black was unburnt fuel.

  7. #7

    Re: White Smoking Knuckle

    The aluminum "knuckles" and the valve lifter bodies have to maintain their tight seal to the pushrod tubes. Oil is pumped up to the heads by the inlet oil pump through the "Y" oil pipe on the outside of the engine from the crankcase to the heads.
    The pistons' rise creates a vacuum under the pistons, which is the main agent to circulate oil through the Knucklehead engine. The rotary "breather valve" turns to intermittently use this vacuum in the camchest to pull the oil back down from the heads and past the lifters by drawing the oil squirted directly on the Big End Bearings off the walls of the crankcase (the at the "scraper" in the back of the crankcase) where it is slung by the centrifugal force of the turning flywheels, through a passage by vacuum and into the camchest.
    There, it joins the oil drawn down the pushrod tubes out of the heads and collects in the bottom in the oil return gear pump, which sends it back to the oil tank. There are several ways for the system to leak oil. Incomplete sealing being number one. Clogged oil return pipes on the outside of the "tins" is another. Those four pipes act just like drinking straws, sucking oil from the tops of the heads and down the valve cover.
    The whole complicated design was a holdover from the original air-cooled radial airplane engines: like the Lycoming and Curtiss-Wright, that were just being proven in the 1920s, that Harley engineers used to model their v-twin OHV Knucklehead motor.
    The vee was, basically, the top two cylinders of a 360º radial engine reduced in size and grafted to a Harley-Davidson crankcase, but the designers (unnecessarily) retained the vacuum-return system that pulled oil up from the upside-down cylinders on the radial engine they copied. Without the vacuum-return, NO oil would return from the lower cylinders on a radial (which were still famous for oil-leaking), but Harley didn't learn to rely on old-fashioned gravity until the Panhead engine, with its oil-return passage down the side of the cylinder, in 1948.
    Sarge, Gerry Lyons, Fla.
    AGENT ORRNGE Survivor. So far.
    The Friendly Fire that Keeps on Burnin'.
    F.O.G. member:
    "It's a 1937, and the downside is, it's out of warranty"

  8. #8

    Re: White Smoking Knuckle

    Thanks guys for the replyes, specially to you Sarge for your time
    Will have a look and see if I got any leaks.
    Charles: the pump is bought from Throttle masters (Ebay)
    The winter is around the corner and it would be nice to get one trip around the block this year before the first snow
    Will give you guys info when I have sourced the problem


  9. #9

    Re: White Smoking Knuckle

    So are you getting good flow back to tank ? If it's flowing it's working , I have a 48 pump , which besides the extra screw and block off plate is the same design up to 1999 . If a compression ring is upside down it will smoke like hell .

  10. #10

    Re: White Smoking Knuckle

    Hi Adam.

    That's the reason im not freaking out I got oilflow coming back to tank so I know I got some lubrication, also got oil coming up to the heads thru the Y-pipe


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